Some power metal oxide semiconductor field effect transistors (MOSFETs) may be vertical devices that have a drain below a vertical drift region with a back side contact, a gate, a body, and a source above the vertical drift region. There may be vertical trenches in the semiconductor material that is typically silicon, that have polysilicon filler therein on opposite sides of the vertical drift region of the MOSFET known as field plates, that may also be referred to elsewhere as RESURF trenches. The field plates contain a dielectric trench liner on sidewalls of the semiconductor.
The power MOSFET can be configured as a planar gate structure formed above the semiconductor surface similar to a conventional MOSFET. Alternatively, the power MOSFET can configured as a trench gate structure where a second polysilicon gate sits on top of polysilicon inside a gate trench etched in the semiconductor material such as silicon. In this power MOSFET structure, also called a trench-MOS, the gate electrode is buried in the gate trench.